Single-walled carbon nanotubes (SWNTs) have attracted much attention due to their great potential for post-silicon electronics. Ultra-thin SWNT networks have been successfully demonstrated as promising and low-cost materials for field-effect transistors (FETs). Nevertheless, high-performance solution-processable SWNT networks, which are suitable for printable electronics, still demand more investigations. The major hurdle to obtain high-performance SWNT-network FETs is the difficulty in obtaining high mobility and highly semiconducting devices due to the co-existence of metallic (M) and semiconducting (S) tubes in the SWNT-network.
Attempts to separate M-SWNTs and S-SWNTs, to specifically grow S-SWNTs, and to enhance the semiconducting characteristics of the devices by application of chemical treatments on SWNTs or devices, however, are achieved with limited success in high-yield and high-reproducibility of device fabrication. Recently, semiconducting FET devices based on tens-nm-thick SWNT films using the nanotubes treated with density gradient ultra-centrifugation (DGU) or modified with organic diazonium salts, or modified with organic radicals have been fabricated. The advantage of using thick SWNT film (tens-nm thick) is to increase the percolation paths and to reduce the device-to-device variations. But the performance (e.g. mobility) of such devices are compromised by the presence of surfactants. Surfactants are usually used for the device fabrication owing to their high efficiency in dispersing SWNTs. They are widely used for DGU-based and dielectrophoresis-based separation techniques. However, the residual surfactant molecules degrade the electrical performance of SWNT devices by increasing the electrode-nanotube resistance, the local electrostatic environments of the SWNTs, and the inter-tube resistance which is the dominanting factor to restrict the conductance of SWNT network.